A hydrogen-absorbing alloy is disclosed in Patent Document 1. As stated in Patent Document 1, when using a fuel cell as an electric power supply for driving a device, it is essential that hydrogen, which is a fuel for the fuel cell, should be handled with care. As a method of safely handling hydrogen, it is especially preferable that hydrogen be absorbed in hydrogen-absorbing alloys, and study has been made on such hydrogen-absorbing alloys. As such alloys, alloys containing Mg and Ni are used, as described in Patent Document 1.
On the other hand, a hydrogen sensor utilizing the characteristics of a hydrogen-absorbing alloy has been developed, wherein a thin layer (thin film) of magnesium-nickel alloy or the like having a light control function is formed on a surface of a substrate made of glass, acrylic resin or the like, and the thin layer is hydrogenated (property of the thin layer is changed) quickly by the action of a catalyst layer (catalyst film) containing palladium or the like. The hydrogen sensor detects change in optical reflectance (hereinafter referred to merely as “reflectance” or, where appropriate, as “optical transmittance”) accompanying the hydrogenation of the thin layer, to thereby detect hydrogen gas leaked into an atmosphere. Also, since the thin layer is hydrogenated in a reversible fashion at normal temperature, a hydrogen gas leak can be safely and quickly detected.
No matter whether the hydrogen-absorbing alloy is used in an electric power supply or in a hydrogen sensor, there has been a demand for hydrogen-absorbing alloys of which the required time from the absorption of hydrogen, or hydrogenation, to the desorption of hydrogen, or dehydrogenation, is shorter, in order to improve the performance of the electric power supply or hydrogen sensor. In the application of hydrogen-absorbing alloys to hydrogen sensors in particular, there has been a demand for hydrogen-absorbing alloys that enable a hydrogen sensor to be used repeatedly at short intervals of time so that after the detection of hydrogen at one location, the hydrogen sensor can be used in a short while at a different location to detect the presence of hydrogen. However, the hydrogen-absorbing alloy disclosed in Patent Document 1 and many of similar hydrogen-absorbing alloys reported so far are intended to improve the hydrogen absorption capacity or the handleability and are not intended to shorten the time required to complete the desorption of hydrogen, or dehydrogenation.